[hctaw]

It's a laborious process that has a significant impact on tone. You usually have to restring the guitar when you change them out.

The biggest change would be between dual coils ("humbuckers") and true single coils. Most modern humbuckers have four leads (you only need two to make a sound, you get two leads per coil) which allow you to wire a switch on the guitar called a "coil tap" which allows you to disengage the secondary coil. This allows you to have a dual coil that functions sonically as either, and it is very desirable for musicians that need a diverse range of tones for their set list (good example is if you ever play a wedding and take requests).

You're also never happy with it. I've changed all the pups on my three guitars multiple times.

[TylerE]

Coil splits are very useful, but they never REALLY quite get there. Even when the secondary coil is off, there's still additional magnetic drag/pull on the string.

A good true single coil has this chime to it that I never get from a split (or tapped) 'bucker.